Robust Predefined-Time Frequency and Voltage Control for AC Microgrid Under Disturbances

This paper proposes a robust distributed secondary control strategy for AC microgrids (MGs) that ensures voltage and frequency regulation within a predefined time limit, while effectively mitigating external disturbances. The proposed composite controller integrates the predefined time convergence approach with a fixed-time integral sliding mode control (ISMC) design. The ISMC enhances disturbance rejection, while the predefined time technique guarantees that all system trajectories reach their desired values within a user-specified timeframe, independent of initial conditions. This ensures accurate regulation of distributed generators’ voltages and frequencies, along with optimal active power sharing and equalized reactive power allocation. Theoretical analysis based on Lyapunov stability confirms the convergence and robustness of the proposed scheme. Multiple simulation and hardware-in-the-loop case studies validate the superior performance of the proposed method over existing time-based controllers, achieving up to 66% lower voltage ITSE and 91% lower frequency ITAE. This confirms its fast restoration capability and strong disturbance rejection across diverse operating conditions.